One of the most common and pertinent criticisms about the performance capabilities and potential of electronic input devices have been their lack of feedback response, for example, kinesthetic feedback. This insufficiency lessens the relationship between man and machine and hinders the depth, expression, and complexity of the data that can be used as input with an electronic device. For example, electronic music instruments lack kinesthetic feedback which hinders an electronic instrument from attaining the status of a “real,” acoustic-like, performance-savvy instrument. However, when applied incorrectly, kinesthetic feedback may make the input device uncomfortable and unfit for expressive input.
In the past, efforts have been made to introduce force feedback into the realm of electronic input devices. One of the earliest experiments, the “Belly-Web” by Michel Waisvisz, was an instrument based on a wire lattice similar to a spider's web. With Waisvisz's interface, simple and intuitive finger movements pushing on wires are made to alter the tension of the wires. The alterations are detected by resistive sensors. The resulting changes are then translated into a set of control variables. Another experiment was the “Harmonic Driving.” This experiment utilized a large compression spring attached to the steering gear of a bicycle in order to control/drive musical events. The spring's bending angles are measured using capacitive sensors that detect the relative displacement between two adjacent coils while torsion is obtained with a potentiometer that rotates as a function of the relative angle between the top and bottom of the spring. More recently other controllers have been introduced that address the issue of force feedback, such as the “Sonic Banana” and the “G-Spring.” The Sonic Banana uses four bend sensors linearly attached to a 2-foot long flexible rubber tube. When bent, the Sonic Banana maps the data from the sensors to sound synthesis parameters. Due to the relative softness of the rubber tube, this controller offers limited feedback when compared to the G-Spring, which measures bend as well. The G-Spring features a heavy 25-inch close-coil expansion spring, and uses light-dependent resistors to measure the varying amount of light that slips through the coils as a function of the amount of bend. Variations in bend are then mapped to synthesis parameters.
These previous device only capture limited parameters, such as the degree to which a controller is flexed. As such, these controllers cannot properly interpret the full expression of input from a user. Further, previous electronic controller designs using springs have been uncomfortable and limited. For example, the design of the G-Spring prevents the addition of individual finger controls and is in accurate when the spring is bent in certain directions.